Methods and apparatus for completing production wells

ABSTRACT

This application discloses new and improved methods and apparatus for completing production wells having perforations which either are to be cleaned or penetrate earth formations which are to be fractured, acidized, or treated such as, for example, to inhibit the subsequent production of unconsolidated formation materials. To practice the present invention, a new and improved production tool is arranged for coupling into a string of production tubing and includes a typical well packer coupled to an elongated tubular member defining an enclosed chamber of a substantial volume and which is initially maintained at a reduced pressure by new and improved normally closed pressure-actuated valves arranged at the opposite ends of the tubular member and adapted to be selectively opened in succession. The production string and the tool are installed in a cased well bore with the packer being set above a previously perforated interval traversing an earth formation which is to be subsequently produced. Once the customary wellhead equipment is installed to provide selective communication from the surface with the tubing and casing, the first of the two normally closed valves is selectively opened by increasing the pressure of the well bore fluids in the annulus above the packer. Upon opening of this first valve, formation fluids will be suddenly exhausted into the reduced-pressure chamber for removing contaminants that may have previously entered the formation following the perforation of the casing so as to leave only uncontaminated formation materials immediately surrounding the perforations. Thereafter, the second normally closed valve is selectively opened by injecting selected fluids by way of the production string through the perforations and into the adjacent earth formations.

United States Patent Primary Examiner-Joseph H. McGlynn Attorneys-ErnestR. Archambeau, Jr., David L. Moseley,

Edward M. Roney and William R, Sherman ABSTRACT: This applicationdiscloses new and improved methods and apparatus for completingproduction wells having perforations which either are to be cleaned orpenetrate earth formations which are to be fractured, acidized, ortreated such as, for example, to inhibit the subsequent production ofunconsolidated formation materials. To practice the present invention, anew and improved production tool is arranged for coupling into a stringof production tubing and includes a typical well packer coupled to anelongated tubular member defining an enclosed chamber oli'a substantialvolume and which is initially maintained at a reduced pressure by newand improved normally closed pressure-actuated valves arranged at theopposite ends of the tubular member and adapted to be selectively openedin succession. The production string and the tool are installed in acased well bore with the packer being set above a previously perforatedinterval traversing an earth formation which is to be subsequentlyproduced. Once the customary wellhead equipment is installed to provideselective communication from the surface with the tubing and casing, thefirst of the two normally closed valves is selectively opened byincreasing the pressure of the well bore fluids in the annulus above thepacker. Upon opening of this first valve, formation fluids will besuddenly exhausted into the reduced-pressure chamber for removingcontaminants that may have previously entered the formation followingthe perforation of the casing so as to leave only uncontaminatedformation materials immediately surrounding the perforations.Thereafter, the second normally closed valve is selectively opened byinjecting selected fluids by way of the production string through theperforations and into the adjacent earth formations.

Patented Dec. 14, 1971 3,627,049

4 Sheets-Sheet 1 W FIG. 2 27 FIG! Y A Y David E. Young INVENTOR ATTORNEYPatented Dec. 14, 1971 4 Sheets-Sheet 2 FIGS David E. Yo ung IN VE N TORATTORNEY AL Patented Dec. 14, 1971 4 Sheets-Sheet 4 FIGIO David E. YoungIN VE N TOR A TTORNE Y METHODS AND APPARATUS FOR COMPLETING PRODUCTIONWELLS It is, of course, customary for a cased well bore to be perforatedat one or more points to provide fluid communication with selected earthformations therearound. Once the well is perforated, various treatingoperations-such as acidizing, fracturing, or sand-consolidatingoperationsare typically conducted to prepare the well for efficientproduction. Those skilled in the art will appreciate, however, that itis not at all uncommon for one or more of the perforations along a givenperforated interval to be at least partially blocked by loose formationmaterials, debris, or foreign matter which is usually deposited in aperforation by typical shaped charges. A partial or total blockage ofone or more of the perforations will, of course, impede or prohibit theintroduction of treating fluids into those perforations and result inthe inadequate treatment of at least those portions of the earthformation immediately adjacent thereto. As a result, further andotherwise needless treating operations will ultimately be required.Accordingly, unless all of the perforations along a perforated intervalare capable of readily conducting fluids, subsequent treating operationsas well as the production rate ofthe well will be significantlyimpaired.

Heretofore, such treating operations have had to be conducted before thedrilling rig is removed from the well site so that its associatedequipment and drill string could be employed. This, of course, resultsin needless expenses as well as additional delays before the productionstring and the related surface equipment can be installed to prepare thewell for production.

Accordingly, it is an object of the present invention to provide a newand improved methods and apparatus for completing wells to obtainimproved fluid communication between the well bore and selected earthformations traversed thereby without delaying the installation of theproduction string and the associated wellhead and surface equipment oncethe drilling operation is concluded.

This and other objects of the present invention are attained by tandemlyarranging upper and lower pressure-actuated valve means at spacedintervals in a production string including a production packer. Theupper and lower valve means are initially closed to define an enclosedchamber of selected volume in the interconnecting tubing therebetweenwhich is maintained at a reduced pressure until after the packer is setand the production string is installed and connected to the usualwellhead and surface equipment. When the well is to be prepared forproduction, the lower valve means are selectively opened from thesurface to draw formation fluids into the enclosed chamber for clearingthe perforations below the production packer of debris or contaminantsthat would otherwise impair fluid communication between the productionstring and the perforated earth formations. Thereafter, the upper valvemeans are selectively opened for injecting fluids from the surface intothe well bore below the packer as may be necessary to prepare the wellfor production.

In the preferred embodiment of the apparatus of the present invention,the lower valve means are operatively arranged to be selectively openedin response to a predetermined change in the pressure in the wellannulus above the production packer. In this manner, communication canbe selectively established between the perforated interval and theenclosed chamber below the upper valve means thereabove. Similarly, inthe preferred embodiment of the apparatus of the present invention, theupper valve means are operatively arranged and adapted to be selectivelyopened in response to a predetermined change in the pressure in theproduction string above the upper valve means for establishingcommunication between the production string and the perforated intervalof the well bore below the packer.

The novel features of the present invention are set forth withparticularity in the appended claims.

The invention, together with further objects and advantages thereof, maybe best understood by way of the following description of new andimproved apparatus and exemplary methods employing the principles of theinvention as illustrated in the accompanying drawings, in which:

FIG. ll, 3 and 5 schematically depict the successive steps of themethods of the presentinvention;

FIG. 2, 4 and 6 respectively show a typical perforation as it may appearduring the course of a completion operation being conducted inaccordance with the methods of the present invention; and

FIG. 7-10 depict preferred embodiments of the new and improved apparatusof the present invention.

Turning now to FIG. 1, a new and improved production tool 20 arranged inaccordance with the principles of the present invention is schematicallyillustrated as being dependently coupled from the lower end of a stringof production tubing 21 and positioned in a well bore 22 having a casing23 secured in place by an external sheath of cement 24. To gaincommunication with an earth formation 25 traversed by the well bore 22,one of more perforations, as at 26, have been previously producedthrough the casing 23 and cement 24 in the usual manner. As iscustomary, the production tubing is dependently supported in the wellbore 22 by a typical wellhead assembly 27 including at least a pair ofvalves, as at 28 and 29, for selectively controlling communication withthe tubing string 21 and casing 23.

As illustrated in FIG. 1, the tool 20 is comprised of a selectivelysettable production packer 30 which is dependently coupled to the lowerend of a tubular body 31 to provide an enclosed chamber 32 that isinitially maintained at a low or atmospheric pressure by arrangingnormally closed valve means 33 and 34 at the upper and lower ends of thebody which are respectively adapted to be selectively openedindependently of one another. As a matter of convenience, it is, ofcourse, preferred to employ one or more joints of conventionalproduction tubing for the elongated body 31. The chamber 32 can, ifdesired, be filled with an inert gas that is at a selected pressurewhich is less than the anticipated formation pressure. Although otherwell packers may, of course, be employed, it is preferred that thepacker 30 be one of the production packers shown in either US. Pat. No.3,074,484 or 3,352,362.

As will be subsequently discussed the methods of the present inventionare uniquely applicable for performing acidizing and fracturingoperations as well as sand-consolidation operations after the productionstring 21 and wellhead 27 are in position. However, for purposes ofillustration, FIGS. 2-6 depict the practice of the methods of thepresent invention as it might be conducted for a sand-consolidationoperation. Accordingly, as depicted in FIG. 2, an enlarged view is shownof one of the perforations 26 as it may well appear where the adjacentformation 25 is substantially unconsolidated or incompetent.

It will, of course, be appreciated that when a perforating tool (notshown) which typically includes one or more shaped charges is positionedin the well bore 22 and actuated for producing the perforations 26, theperforations will initially extend into the incompetent formation 25 asgenerally represented in FIG. 2. It is believed, however, by thoseskilled in the art that the perforation 26 will quickly fill up withloose materials from the incompetent formation 25 leaving open only apassage or so-called tunnel 35 extending through the casing 23 and theadjacent cement sheath 24.

In any event, irrespective of the nature of the formation, debris (suchas. at 36) will be left in the formation 25 as a result of thedisintegration of a typical shaped charge liner. Moreover, by observingtest shots fired into laboratory targets, it is known that a typicalshaped charge perforating jet will leave a somewhat-impermeable layer ofdebris (as indicated at 37) around the walls of the forward portion ofthe perforation 26. This relatively impermeable sheath of debris willeither remain substantially in the position illustrated at 37; or, ifthe formation (as at 25) is incompetent, this impermeable layer willmost likely be collapsed inwardly as the forward portion of theperforation 26 is filled with loose formation materials.

In any event, flow communication between the entrance tunnel 35 and theformation will be at least retarded, if not substantially impaired, bythe debris 36 and 37 deposited in the formation just outside of thetunnel. It is, therefore, this debris 36 and 37 which, irrespective ofthe competency of the formation 25, must be removed before the well bore22 can be successfully completed and production commenced.

' Accordingly, as illustrated in FIG. 3, after the packer has been setfor isolating the interval of the well bore 22 immediately adjacent tothe perforations 26 from the remainder of the well bore thereabove andthe wellhead 27 is in position, the lower valve 34 is opened. It will beappreciated, therefore, that upon opening of the lower valve 34, asudden hgih-pressure difierential is developed between the connatefluids in the formation 25 and the enclosed chamber 32 which,preferably, is initially at atmospheric pressure. This sudden pressuredifferential across the perforated well bore interval will induce arapid, high-velocity flow of connate fluids, as at 38, from theformation 25 through the various entrance tunnels 35 and into the emptychamber 32. These rushing fluids will, therefore, effectively wash outthe debris, as at 36 and 37 (FIG. 2), along with a limited quantity ofloose formation materials through the several tunnels 35. As a result,as shown in FIG. 4, once this sudden flow ceases upon the filling of thechamber 32, the formation 25 surrounding the perforations 26 will beeffectively cleaned leaving only clean formation particles, as at 39,partially or totally filling the tunnels 35 through the casing 23 andcement 24.

It will be recognized, of course, that with even these clean formationparticles, as at 39, in the entrance passages 35, the subsequentinjection of consolidating agents or the production of connate fluidsfrom the formation 25 will be materially limited. It is, therefore, oneof the paramount objects of the present invention to remove theseloosened particles 39 from the tunnels 35 before further completionoperations are conducted.

Accordingly, to accomplish this, a clean fluid, as at in FIG. 5, isadmitted to the production string 21 by way of the wellhead valve 28;and, by opening the upper valve 33, suddenly introduced into thepreviously closed chamber 32 to produce a sudden shock or transitorypressure surge in the isolated interval of the well bore 22 below thepacker 30 for driving the clean sand particles 39 back into theformation 25 and clearing the tunnels 35 as illustrated in H0. 6.

It will, of course, be appreciated that although the chamber 32 may becompletely filled with the connate fluids 38 upon opening of the lowervalve 34, these fluids as well as those in the isolated portion of thewell bore 22 below the packer 30 will be at a pressure no greater thanthe natural formation pressure of the earth formation 25. Accordingly,by rapidly opening the upper valve 33, the injection fluid 40 will besuddenly moved downwardly into the chamber 32 and develop significantdynamic shock pressure which are substantially greater than theformation pressure of the well fluids within the isolated portion of thewell bore 22 below the packer 30. Thus, as previously noted, the suddenrelease of the injection fluid 40 into the chamber 32 will be effectivefor forcibly driving the sand particles 39 out of the several tunnels 35and back into the surrounding formation 25. It will, of course, beappreciated that once these transitory shock pressures have subsided,the injection fluid 40 is maintained at an elevated pressure which willbe sufficient for preventing the production of further connate fluidsthrough the several perforations 26 so that additional sand particleswill not reenter the several tunnels 35.

Where the formation 25 does not require a consolidation operation, theinjection fluid 40 needs only to be a suitable fluid such as a cleansaline solution. By properly selecting a saline solution of sufficientdensity, the resulting hydrostatic pressure of the injection fluid 40will alone be effective for retaining control of the well untilproduction is commenced.

On the other hand, where the earth formation 25 is to be consolidated bytypical sand-consolidating agents, it is generally preferred that theinjection fluid 40 be a so-called preflush fluid" such as kerosene,diesel oil, or a clean saline solution. This injection fluid 40 ismaintained at an elevated pressure before the upper valve 33 is opened;and once the pressured preflush fluid 40 is pumped into the formation25, one or more consolidating agents (not shown) are successively pumpedthrough the tubing string 21 and into the formation to accomplish thedesired consolidation. As is typical, if production is not to becommenced immediately, the consolidating fluids may then be followed bya suitable after-flush agent, such as kerosene, as well as in someinstances, temporary plugging agents such as Black Magic an oil-base mudas supplied by Oil Base, lnc., of Houston, Tex. It will be recognizedthat the hydrostatic pressure and the pumping pressure of thesesuccessively injected treating fluids will be greater than the formationpressure of the formation 25 so that the tunnels 35 will remain openthroughout the consolidation operation. The particular nature or type ofthe sand-consolidation agents employed are, of course, of nosignificance to the present invention and the consolidating agents maybe either porous-setting or solid-setting plastics.

As previously mentioned, the methods of the present invention are alsoequally applicable for acidizing or hydraulic fracturing operationsafter the wellhead 27 and the production string 21 are in position.Accordingly, where the formation 25 is to be either acidized orfractured, the treating fluid 40 will, of course, be the fluid or fluidswhich are typically employed for such operations. Otherwise, thesequence of events will be substantially as depicted in FIGS. 1-6 withthe possible exception that the formation 25 may be sufficientlycompetent that there will be little or no loose formation materials, asat 39, drawn into the tunnels 35 as the debris 36 and 37 is cleared fromthe perforations 26. In either situation, however, those skilled in theart will appreciate that the new and improved methods of the presentinvention will be of significant benefit for economically conductingeither an acidizing operation or a hydraulic fracturing operation.

Of particular significance, it should be recognized that by employingthe methods of the present invention to commence either an acidizingoperation or a fracturing operation, the dynamic shock or surgepressures that are developed when the treating fluid 40 is suddenlyreleased upon opening of the upper valve 33 will be of material benefitin commencing the operation. This sudden surge or pressure shock will,therefore, be particularly useful in breaking down" the formation 25 toassure that the treating fluid 40 is entering all of the perforations26. AS a further benefit, it has been found that the pumping pressuresrequired to continue movement of the treating fluid 40 into theformation 25 will be significantly reduced in comparison to the pumpingpressures normally required for conducting acidizing or fracturingoperations as heretofore conducted before the present invention.

it should be noted that where the methods of the present in vention areused for sand-consolidating operations, a sufficient pressure surge orshock will usually be developed even where the chamber 32 is completelyfilled before the upper valve 33 is opened. On the other hand, where anacidizing operation or fracturing operation is being conducted inaccordance with the methods of the present invention, it has been foundthat greatly enhanced surge or shock pressures will be obtained byarranging the interconnecting tubing 31 to have a volumetric capacity(i.e., the chamber 32) that is greater than the anticipated volume ofthe connate fluids 38 that will enter the chamber during thepredetermined time interval before opening the upper valve 33. In thismanner, the upper portion of the chamber 32 will be empty when the uppervalve 33 is opened; and the sudden entrance of the treating fluid 40into the still-empty upper portion of the chamber will produce acorresponding substantial imploding force which in turn develops thegreatly enhanced shock forces referred to above.

Turning now to FIGS. 7 and 8, a preferred embodiment is shown of thelower valve 34 which is particularly adapted for 101014 outs practicingthe methods of the present invention. As best seen in FIG. 7, the valve34 includes a tubular body 41 having threads 42 and lower ends andsuitably adapted for tandemly coupling the valve between the packer 36and the interconnecting tubing 311. In the preferred embodiment of thevalve 34, a transverse barrier 44 is arranged across the axial bore 45of the valve body 411 and, for reasons that will subsequently beexplained, releasably coupled to the valve body by means such as alateral pin 46 having a predetermined strength. A sealing member, suchas an O-ring 47 arranged around the barrier 44, fluidly seals thebarrier in relation to the valve body 411 to block fluid communicationthrough the axial bore 45.

To provide selective fluid communication through the axial bore 43 whenthe barrier 44 is positioned therein, longitudinally spaced lateralports 43 and 49 are provided in the valve body 41 above and below thebarrier; and an elongated sleeve 50 is slidably mounted around the valvebody and cooperatively arranged for longitudinal movement thereonbetween a first position blocking fluid communication between thelateral ports and a second position in which the ports are incommunication with one another. In the preferred embodiment of the valve34, the body 41 is arranged as upper and lower tandemly coupled sections51 and 52, with the ports 43 and 49 being in the upper section and thelower section having an enlargeddiameter portion 53 extending upwardlyaround the lower ports and defining an upwardly facing annular space 54therearound. The lower portion of the sleeve Sill is enlarged, as at 55,and complementally fitted in the annular space 54, with inner and outersealing members 56 and 57 cooperatively arranged thereon for fluidlysealing the enlarged portion of the sleeve in the annular space to blockfluid communication between the lateral ports 48 and 49 so long as theenlarged sleeve portion is positioned therebetween. The upper portion ofthe sleeve 50 is extended above the upper port 48 and a sealing member53 is cooperatively arranged on an inwardly enlarged upper portion 59 ofthe sleeve for sealing engagement with the exterior surface 60 of theupper section 51 above the upper port for isolating the port from thewell bore fluids. To releasably secure the sleeve 50 in its elevatedposition depicted in FIG. 7, means are provided such as a pin 61 of apredetermined strength for releasably coupling the sleeve to the valvebody 41.

Accordingly, so long as the valve 34 is in the position depicted in FIG.7, the barrier 44 will block fluid communication through the axial bore45 and the ports 48 and 49 bypassing the barrier will each be isolatedfrom one another by the sleeve 50 and the coaction of the sealingmembers 56-58 with the exterior surface 60 of the valve body 4]. Itwill, therefore, be appreciated from FIGS. 1 and 7, that when the valve34 is in its initial position and operatively coupled into the tool 20ofthe present invention, the axial bore 45 above the barrier 44 will beat a reduced pressure (i.e., whatever pressure is initially maintainedin the enclosed chamber 32) and the lower portion ofthe axial bore belowthe barrier will be in communication with the fluids in the well bore 22below the packer 30. Thus, to prevent the resulting upwardly actingpressure forces imposed by the well bore fluids on the barrier 44 fromweakening or prematurely failing the pin 46, it is preferred to providean inwardly directed shoulder 62 in the axial bore 45 against which theupper end of the barrier is initially abutted. It will be recognized, ofcourse, that the shoulder 62 will permit the pin 46 to be much weakerthan would otherwise be possible if the barrier 44 was not abuttedagainst the shoulder.

Those skilled in the art will, of course, appreciate that the sleeve 50will be subjected to a downwardly acting pressure force imposed on theeffective cross-sectional area defined between the O-rings 57 and 53 aswell as an upwardly acting pressure force imposed on the effectivecross-sectional area defined between the O-rings 56 and 57. By arrangingthe upper body section ll to have a uniform diameter along the exteriorsealing surface 60, these upwardly acting and downwardly acting pressureforces will be independent of the 43 respectively arranged on its upperand pressure in the enclosed chamber 32 so that the net unbalancedpressure force acting at any time on the sleeve 50 will be directlyrelated to the pressure differential across the production packer 30 atany given time.

Accordingly, it will be appreciated that the lower valve 34 can beselectively opened as illustrated in FIG. 3 by increasing the pressurein the well bore 22 above the packer 30 in relation to the pressurebelow the packer to impose :1 corresponding downwardly acting pressureforce on the sleeve 50. This is, of course, readily accomplished fromthe surface by opening the wellhead valve 29 and applying sufficientpumping pressure to the fluids in the well bore 22 above the packer 30to cause the failure of the pin 61 retaining the sleeve 50 in itsinitail elevated position as shown in FIG. 7. It will, of course, beappreciated from F IG. 8 that once the pin 61 fails to allow the sleeve30 to be moved downwardly in relation to the valve body M by theseunbalanced pressure forces, the ports 48 and 49 will be placed intocommunication with one another to permit the fluids in the well bore 22and the formation 25 below the packer 36 to rush into the enclosedchamber 32 as previously described in reference to FIG. 3. To facilitatefluid communication between the ports 48 and 49, the internal bore ofthe sleeve 30 is enlarged, as at 63, between the seals 56 and 53.

As illustrated in FIG. 8, to prevent the sleeve from inadvertentlyreturning to its initial position, latching means are provided such asan outwardly expansible: ring 64 which is initially confined in acircumferential groove 65 around the body 41 by the upper portion of thesleeve 50 and is operatively arranged to expand outwardly once thesleeve is moved downwardly. In the preferred manner of arranging theexpansible ring 64, the groove 65 is formed at the upper end of thesealing surface 60 and the adjacent internal surface of the sleeve 50 iscomplementally shaped to define therein an upwardly directed shoulder 66adapted to abut the lower surface of the contracted ring while thesleeve is in its elevated position shown in FIG. 7. As a result,upwardly directed forces on the sleeve 50 before the valve 34 is to beopened will be incapable of inadvertently shifting the sleeve upwardly.Once, however, the expansible ring 64 is unconfined and expandsoutwardly to the position shown in FIG. 8, its lower surface will engagethe shoulder 67 defined by the upper end of the sleeve 50 to permanentlyretain the sleeve in its illustrated downward position.

Turning now to H0. 9, a preferred embodiment of the upper valve 33 isdepicted in its initial closed position as previously described withreference to FIG. ll. As illustrated in FIG. 9, the upper valve 33includes a tubular body 68 having a transverse barrier 69 that isinitially positioned in the axial bore 70 of the body and fluidly sealedin relation thereto, as by sealing members 711, for initially bloclkingfluid communication through the axial bore. in the preferred embodimentof the upper valve 33, the barrier 69 is releasably secured to the valvebody 66 by a plurality of balls 72 which are loosely confined in lateralopenings 73 formed around the body and appropriately sized to projectinto the axial bore 70 so as to be partially received in a complementalgroove 74 formed around the barrier. Thus, it will be appreciated thatso long as the balls 72 are cooperatively engaged in the circumferentialgroove 74, the barrier 69 is securely retained against axial movement inrelation to the body 68.

To selectively retain the balls 72 in the circumferential groove 74, asleeve 75 is slidably mounted around the valve body 63 and releasablysecured thereto, as by a lateral pin 76 of predetermined strength, forinitially positioning the internal surface 77 of the sleeve over thelateral openings 73. Thus, so long as the internal surface 77 of thesleeve 75 is covering the lateral openings 73, the balls 72 thereincannot be withdrawn from the circumferential groove 74 and the barrier69 will be retained in position to block fluid communication through theaxial bore 76 of the upper valve 33. By forming a circumferential groove76 around the internal wall of the sleeve 75 that is spaced above thesurface 77 and of sufficient depth to enable the balls 72 to moveoutwardly out of the circumferential groove 74, upon downward movementof the sleeve to bring the groove 78 into alignment with the openings 73the barrier 69 will be free to move downwardly in relation to the valvebody 68.

In the preferred manner of selectively releasing the balls 72 from thebarrier 69, the upper end of the sleeve 75 is extended upwardly into adownwardly directed annular cavity 79 formed around the body 68. In thepreferred embodiment of the valve 33, the valve body 68 is comprised oftandemly coupled tubular sections 80 and 81, with the upper body sectionhaving an enlarged-diameter 'portion 82 extending downwardly around thelower body section and spaced outwardly therefrom to define the annularspace 79. The upper end of the sleeve 75 is fluidly sealed within theannular space 79 by seals, such as O-rings 83 and 84, mounted around theinner and outer walls of the sleeve; and a lateral port 85 is providedin the body 68 to communicate the axial bore 70 above the barrier 69with the enclosed upper portion of the annular space above the O-rings83 and 84. An expansible ring 86 is mounted in a complementary annulargroove 87 formed around the sleeve 75 and operatively located to retainthe ring in the annular space 79 so long as the sleeve is secured in itselevated position depicted in FIG. 9 by the shear pin 76.

It will be appreciated, therefore, that the barrier 69 will be securedin its flow-blocking position in the axial bore 70 so long as the sleeve75 is cooperatively retaining the balls 72 in the circumferential groove74 around the barrier. Thus, so long as the shear pin 876 maintains thesleeve 75 in its elevated position, the barrier 69 will be securelylatched to the valve body 68 by the balls 72 and the sleeve.Accordingly, to open the upper valve 33, the pressure in the axial bore70 above the barrier 69 must be increased above the pressure of the wellbore fluids above the packer 30 to impose a downwardly acting unbalancedpressure force on the effective cross-sectional area of the sleeve 75defined between the O- rings 83 and 84 that is sufficient to fail theshear pin 76. Once the sleeve 75 is freed and is moved downwardly to itslower position (as determined by the location of an upwardly directedshoulder 88 formed around the body section 81 and spaced below thesleeve), the circumferential groove 78 will be aligned with the balls 72so that they will be cammed outwardly into the groove by the downwardmovement of the barrier 69.

REferring again to FIG. 1, it will be appreciated that when the new andimproved tool of the present invention is positioned in the well bore22, the upper and lower valves 33 and 34 will respectively be in theirnormally closed positions as depicted in FIGS. 7 and 9. The elongatedbody 31 will define the enclosed chamber 32 so long as the barriers 44and 69 remain in position and the sleeve 50 remains in its elevatedposition in relation to the body 41 ofthe lower valve 34.

As previously described in relation to FIG. 3, the lower valve 34 isselectively opened to induce a rapid flow of connatc fluids as at 38into the enclosed chamber 32 for flushing the debris 36 and 37 from theperforations 26. To accomplish this, the wellhead valve 29 is opened andsufficient pumping pressure is applied from the surface to the well borefluids above the packer to fail the shear pin 61 and shift the sleeve 50downwardly to its position illustrated in FIG. 8 for establishing fluidcommunication (by way of the ports 48 and 49) between the enclosedchamber 31 and the well bore 22 below the packer. It will, or course, beappreciated that the barrier 44 will still be retained in its depictedposition by the shear pin 46. Moreover, once the sleeve 50 movesdownwardly, the expansible ring 64 will be partially expanded out of thegroove 65 so as to move outwardly over the upper end 67 of the sleeveand permanently secure the sleeve in its lower position in relation tothe valve body 41.

It will. of course, be appreciated that when the pressure of the wellbore fluids above the packer 30 is increased to UPC" the lower valve 34.the uppcr valve 33 will not be affected since the increased pressurewill only tend to urge the ballretaining sleeve 75 upwardly against theshoulder defined by the upper end of the annular space 79. The barrier69 will, therefore, be securely latched in its initial position asillustrated in FIG. 9 so long as the sleeve 75 is cooperativelyretaining the balls 72 in the barrier groove 74. Thus, the upper valve33 may be left closed as long as is desired after communication has beenestablished through the ports 48 and 49 of the lower valve 34. It will,of course, be recalled that the barrier 44 in the lower valve 34 willstill be in position therein after the ports 48 and 49 are opened.

Accordingly, when it is desired to open the upper valve 33 forintroducing a treating fluid into the chamber 32 as previously describedin relation to FIG. 5, the wellhead valve 28 is opened and an increasedpressure is applied to the fluid 40 in the production string 21 forurging the ball-retaining sleeve 75 downwardly with sufficient force tofail the shear pin 76. As best seen in FIG. 10, once the sleeve 75 isshifted downwardly into abutment with the shoulder 88, the expansiblering 86 will expand partially out of the groove 87 and be received in adownwardly facing groove 89 in the lower face of the enlarged bodyportion 82 so as to permanently latch the ball-retaining sleeve in itslower position.

The barrier 69 will, of course, be released once the balls 72 areshifted outwardly into the sleeve groove 78. It will be noted that inthe preferred embodiment of the upper valve 33, the barrier 69 is madesomewhat smaller than the internal diameter of the axial bore 70 and aslight inwardly enlarged shoulder 90 is formed in the body 68 adjacentto the initial position of the barrier for sealing engagement with theO-rings 71. In this manner, once the barrier 69 is released and passesbelow the shoulder 90, the barrier will be free to move easily throughthe interconnecting tubing 31 to the lower valve 34. Accordingly,although the barrier 69 could just as well be displaced through theinterconnecting tubing 31 by maintaining a substantial pumping pressureon the treating fluid 40 in the production string 21, it is preferred todispose a typical separator plug, as at 91, in the production stringahead of the treating fluid. This will, of course, minimize the pumpingpressure required to move the barrier 69 downwardly through theinterconnecting tubing 31 to the lower valve 34.

Referring again to FIG. 8, it will be recalled that the shear pin 46 andshoulder 62 retained the barrier 44 in position within the lower valve34 when the sleeve 50 was shifted downwardly to place the ports 48 and49 into communication with one another. Thus, the barrier 44 can not bereleased until the pressure of the fluids now in the chamber 32 abovethe barrier 44 is increased above the pressure of the fluids therebelowfor developing a sufficient downwardly acting force on the barrier tofail the shear pin 46. This will, of course, occur once the separatingplug 91 has carried the upper barrier 69 downwardly to the lower barrier44. Hereagain, it should be noted that in the preferred embodiment ofthe lower valve 34, the barrier 44 is of a reduced diameter and thatportion of the axial bore 45 just below the shoulder 62 is slightlyreduced, as at 92, to provide a sealing surface for the O-ring 47. Thus,once the shear pin 46 does fail, the two barriers 44 and 69 will bemoved further downwardly by the separator plug 91 through the packer 30and allowed to fall on into the well bore 22 therebelow. In thepreferred embodiment of the tool 20 of the present invention, it ispreferred to fabricate the barriers 44 and 69 of either a metal such asaluminum or a rigid plastic material which will be ultimatelydisintegrated in time by the corrosive action of the well bore fluids soas to minimize the debris left in the well bore 22.

It will, of course, be appreciated that if the separating plug 91 is notemployed, the lower barrier 44 could also be released from the lowervalve 34 by dropping a so-called sinker bar" (not shown) from thesurface through the production string 21 after the upper barrier 69 hasbeen released from the upper vnlve 33.

In any event. once both of the barriers 44 and 69 have passed throughthe packer 30, a continuous and substantially uninterrupted passage isprovided through the tubing string 21 and the production tool betweenthe wellhead 27 and the well bore 22 below the packer. Thus, anyso-called "through tubing completion or treating operation that istypically conducted in a production well can be readily conducted in thewell bore 22 without having to remove either the wellhead 27 or theproduction tool 20 and its supporting string of production tubing 21!.

Accordingly, it will be appreciated that the present inventionhasprovided new and improved methods and apparatus for completing wells toobtain improved fluid communication between the well bore and selectedearth formations traversed thereby without delaying the installation ofthe production string and the associated wellhead and surface equipmentonce the drilling operation is concluded. By arranging the new andimproved production tool of the present invention into an otherwisetypical production string once the formation interval below the intendedposition of the production packer has been perforated, the wellhead andother associated surface equipment can be installed in the usual mannerwithout further delay. Then, when the well is to be prepared forproduction, the lower valve of the new and improved production tool ofthe present invention is opened to clear the perforations of debris andthe like. Thereafter, a fluid is discharged into the production stringand the upper valve of the production tool is opened to establishcommunication from the surface with the formations below the packer.Where the formations require acidizing, fracturing or consolidationtreatments to prepare the well for production, one or more treatingfluids can be readily dispatched through the now opened productionstring and into the well bore below the packer.

While particular illustrations and embodiments of the present inventionhave been shown and described, it is apparent that changes andmodifications may be made without departing from this invention in itsbroader aspects; and, therefore, the aim in the appended claims is tocover all such changes and modifications as fall within the true spiritand scope of this inventionQ What is claimed is:

l. A method for preparing a well for production of connate fluids from awell bore having a perforated interval with one or more perforationstraversing earth formations and comprising the steps of: coupling upperand lower pressure'actuated normally closed valves at spaced positionsin a string of production piping having a packer coupled thereto fordefining an enclosed chamber in said production string between saidupper and lower valves which is initially at a pressure less than theexpected pressure of said connate fluids so long as said upper and lowervalves remain closed; lowering said production string into said wellbore and setting said packer therein above said perforated interval forisolating said perforated interval from the remainder of said well borethereabove; coupling the upper end of said production string to awellhead for securing said production string in said well bore andproviding selective communication from the surface into said productionstring above said upper pressure-actuated valve and from the surfaceinto the well annulus exterior of said lower pressure-actuated valve andabove said packer; varying the pressure in said well annulus toselectively open said lower pressure-actuated valve and draw saidconnate fluids into said chamber for expurgating said perforations; and,thereafter, varying the pressure in said production string forselectively opening said upper pressure-actuated valve to establishcommunication through said production string between said wellhead andsaid perforated interval.

2. The method of claim ll wherein at least the last of the latter twosteps is not performed until shortly before production is to becommenced from the well.

3. The method of claim ll wherein said dently coupled to said lowervalve.

4. The method of claim l wherein said lower pressure-actu ated valve isopened by increasing the pressure in said well annulus.

packer is depen- Jill 5. The method of claim 4 wherein said upperpressure-actuated valve is opened by increasing the pressure in saidwell annulus.

6. The method of claim 5 wherein said upper pressure-actuated valve isnot opened until production is about to be commenced from the well.

7. The method of claim ll wherein said upper pressure-actuated valve isopened by increasing the pressure in said production string.

a. Apparatus adapted for producing connate fluids from earth formationstraversed by a well bore and comprising: a production string positionedin said well bore between the surface and a perforated interval of saidwell bore having one or more perforations directed into earth formationsadjacent thereto; means adapted for supporting said production string insaid well bore and including a wellhead coupled to the upper end of saidproduction string and operatively arranged for selectively controllingfluid communication from the surface with said production string as wellas with the well annulus exterior of said production string; firstnormally closed valve means coupledin said production string andoperatively arranged for opening in response to changes in the pressuretherein; second normally closed valve means operatively arranged foropening in response to changes in the pressure in said well annulus andcoupled below said first valve means in said production string fordefining an enclosed chamber therein so long as said first and secondvalve means remain closed; and a well packer coupled in said productionstring below said second valve means and operatively arranged forpacking-offsaid well bore above said perforated interval.

9. The apparatus of claim d wherein said first valve means areselectively opened only in response to increases of the pressure in saidproduction string thereabove to at least a predetermined pressure.

10. The apparatus of claim 8 wherein said first valve means include avalve member movable from a first position blocking fluid communicationbetween said production string to a second position openingcommunication therebetween, and a pressure-responsive actuatoroperatively arranged for selectively moving said valve member to itssaid second position upon an increase ofthe pressure in said productionstring to at least a predetermined pressure.

Ill. The apparatus of claim 10 wherein said first valve means furtherinclude latching means operatively arranged thereon for releasablyretaining said valve member in its said first position until saidpressure-responsive actuator is operated.

ll2. The apparatus of claim 8 wherein said second valve means areselectively opened only in response to increases of the pressure in saidwell annulus to at least a predetermined pressure.

113. The apparatus of claim 8 wherein said second valve means include avalve member movable between a normally closed position to an openposition; and a pressure-responsive actuator operatively arranged inrelation to said valve member for selectivelymoving said valve member toits said open position upon increases of the pressure in said wellannulus to at least a predetermined pressure.

114. The apparatus of claim 13 wherein said second valve means furtherinclude latching means operatively arranged thereon for retaining saidvalve member in its said open position once said valve member is movedthereto.

15. Apparatus adapted to be used in a well bore having at least oneperforated interval traversing earth formations from which connatefluids are to be produced and transported to the surface through astring of production piping supported in the well bore by a wellheadoperatively arranged at the surface for selectively controllingcommunication to the production piping and the well annulus exteriorthereof, said apparatus comprising: an elongated body having alongitudinal bore defining a chamber between the upper and lower ends ofsaid body; first valve means coupled to said upper end of said body andadapted for normally blocking [fluid communication between said chamberand a string of production piping coupled thereabove; firstpressure-responsive actuating means operatively associated with saidfirst valve means and adapted for opening said first valve means onlyupon an increase of fluid pressure within a string of production pipingcoupled to said first valve means; second valve means coupled to saidlower end of said body and adapted for normally blocking fluidcommunication between said chamber and a production packer dependentlycoupled therebelow; and second pressure-responsove actuating meansoperatively associated with said second valve means and adapted foropening said second valve means only upon an increase of fluid pressurein the well annulus exterior thereof and above a production packertherebelow.

16. Apparatus adapted to be used in a well bore having at least oneperforated interval traversing earth formations from which connatefluids are to be produced and transported to the surface through astring of production piping supported in the well bore by a wellheadoperatively arranged at the surface for selectively controllingcommunication to the production piping and the well annulus exteriorthereof, said apparatus comprising: first valve means including a firsttubular body adapted to be dependently coupled to the lower end of sucha string of production piping, a fluid barrier sealingly engaged withinsaid first tubular body and adapted for downward movement therefrom toopen communication through said first tubular body, apressure-responsive actuator operatively arranged on said first tubularbody for movement relative thereto between first and second positions,latching means operatively arranged between said actuator and said fluidbarrier for retaining said fluid barrier within said first tubular bodyonly so long as said actuator is in its said first position, and passagemeans on said first tubular body and adapted for communicating pressuretherein above said fluid barrier to said actuator to shift said actuatorto its said second position for releasing said latch means from saidfluid barrier so that said fluid barrier can be moved downwardly fromsaid first tubular body upon an increase of pressure in a productionstring coupled to said first tubular body; a tubular member dependentlycoupled to said first tubular body and having an internal bore adaptedto receive said fluid barrier upon its release from said first tubularbody; and second valve means including a second tubular body dependentlycoupled to said tubular member and adapted for coupling to a productionpacker therebelow for packing-off a perforated interval of a well bore,a transverse barrier arranged within said second tubular body forblocking fluid communication therethrough, upper and lower fluid portsin said second tubular body above and below said transverse barrier, avalve member operatively arranged on said second tubular body andadapted for movement relative thereto between a first position blockingfluid communication between said fluid ports and a second positionestablishing fluid communication therebetween, and pressureresponsiveactuating means operatively arranged on said second tubular body formoving said valve member to its said second position only upon anincrease of the pressure in the well annulus.

17. A valve adapted for coupling to a string of production pipingsupported in a well bore traversing earth formations and comprising: atubular body having a longitudinal bore therethrough; a fluid barriersealingly arranged in said longitudinal bore and adapted for downwardmovement therefrom; actuating means slidably mounted on said tubularbody and adapted for movement relative thereto between first and secondspaced positions; means on said tubular body defining a piston chamber;piston means operatively disposed in said piston chamber and adapted formoving said actuating means from said first position to said secondposition in response to a pressure variation'in said piston chamber;latch means operatively arranged on said tubular body between saidactuating means and said fluid barrier and adapted for releasablysecuring said fluid barrier within said longitudinal bore until saidactuating means move from said first position to said second position;and passage means arranged between said piston chamber and saidlongitudinal bore above said fluid barrier and adapted for communicatingpressure variations in a string of production piping coupled to saidtubular body to said piston means.

18. The valve of claim 17 further including means operable upon movementof said actuating means to said second position for securing saidactuating means in said second position.

19. A valve adapted for coupling to a string of production pipingsupported in a well bore traversing earth formations and comprising: atubular body having a longitudinal bore therethrough; a fluid barrierarranged within said tubular body for blocking fluid communicationthrough said longitudinal bore; upper and lower fluid ports in saidtubular body above and below said fluid barrier; a tubular valve membertelescopically arranged on said tubular body and adapted for movementrelative thereto between a first position blocking fluid communicationbetween said fluid ports and a second position establishing fluidcommunication therebetween; means on said tubular body defining anannular piston chamber around said lower fluid ports; sealing meansarranged on said valve member and operatively disposed within saidpiston chamber for isolating said lower fluid ports from the exterior ofsaid tubular body so that pressures exterior of said tubular body willbe imposed on said valve member for urging said valve member toward itssaid second position; and means releasably securing said valve memberagainst movement to its said second position until the pressures imposedon said valve member exceed a predetermined value.

20. The valve of claim 19 wherein said fluid barrier is movably disposedin said longitudinal bore, and further including means releasablysecuring said fluid barrier in said tubular body and adapted to releasesaid fluid barrier upon application ofa predetermined force on saidfluid barrier.

21. The valve of claim 19 further including means operable upon movementof said valve member to its said second position for securing said valvemember in its second position.

w it s t lUlON (H89

1. A method for preparing a well for production of connate fluids from awell bore having a perforated interval with one or more perforationstraversing earth formations and comprising the steps of: coupling upperand lower pressure-actuated normally closed valves at spaced positionsin a string of production piping having a packer coupled thereto fordefining an enclosed chamber in said production string between saidupper and lower valves which is initially at a pressure less than theexpected pressure of said connate fluids so long as said upper and lowervalves remain closed; lowering said production string into said wellbore and setting said packer therein above said perforated interval forisolating said perforated interval from the remainder of said well borethereabove; coupling the upper end of said production string to awellhead for securing said production string in said well bore andproviding selective communication from the surface into said productionstring above said upper pressure-actuated valve and frOm the surfaceinto the well annulus exterior of said lower pressure-actuated valve andabove said packer; varying the pressure in said well annulus toselectively open said lower pressure-actuated valve and draw saidconnate fluids into said chamber for expurgating said perforations; and,thereafter, varying the pressure in said production string forselectively opening said upper pressureactuated valve to establishcommunication through said production string between said wellhead andsaid perforated interval.
 2. The method of claim 1 wherein at least thelast of the latter two steps is not performed until shortly beforeproduction is to be commenced from the well.
 3. The method of claim 1wherein said packer is dependently coupled to said lower valve.
 4. Themethod of claim 1 wherein said lower pressure-actuated valve is openedby increasing the pressure in said well annulus.
 5. The method of claim4 wherein said upper pressure-actuated valve is opened by increasing thepressure in said well annulus.
 6. The method of claim 5 wherein saidupper pressure-actuated valve is not opened until production is about tobe commenced from the well.
 7. The method of claim 1 wherein said upperpressure-actuated valve is opened by increasing the pressure in saidproduction string.
 8. Apparatus adapted for producing connate fluidsfrom earth formations traversed by a well bore and comprising: aproduction string positioned in said well bore between the surface and aperforated interval of said well bore having one or more perforationsdirected into earth formations adjacent thereto; means adapted forsupporting said production string in said well bore and including awellhead coupled to the upper end of said production string andoperatively arranged for selectively controlling fluid communicationfrom the surface with said production string as well as with the wellannulus exterior of said production string; first normally closed valvemeans coupled in said production string and operatively arranged foropening in response to changes in the pressure therein; second normallyclosed valve means operatively arranged for opening in response tochanges in the pressure in said well annulus and coupled below saidfirst valve means in said production string for defining an enclosedchamber therein so long as said first and second valve means remainclosed; and a well packer coupled in said production string below saidsecond valve means and operatively arranged for packing-off said wellbore above said perforated interval.
 9. The apparatus of claim 8 whereinsaid first valve means are selectively opened only in response toincreases of the pressure in said production string thereabove to atleast a predetermined pressure.
 10. The apparatus of claim 8 whereinsaid first valve means include a valve member movable from a firstposition blocking fluid communication between said production string toa second position opening communication therebetween, and apressure-responsive actuator operatively arranged for selectively movingsaid valve member to its said second position upon an increase of thepressure in said production string to at least a predetermined pressure.11. The apparatus of claim 10 wherein said first valve means furtherinclude latching means operatively arranged thereon for releasablyretaining said valve member in its said first position until saidpressure-responsive actuator is operated.
 12. The apparatus of claim 8wherein said second valve means are selectively opened only in responseto increases of the pressure in said well annulus to at least apredetermined pressure.
 13. The apparatus of claim 8 wherein said secondvalve means include a valve member movable between a normally closedposition to an open position; and a pressure-responsive actuatoroperatively arranged in relation to said valve member for selectivelymoving said valve member to its said open position upon increases of thepressure in said well annulus to at least a predetermined pressure. 14.The apparatus of claim 13 wherein said second valve means furtherinclude latching means operatively arranged thereon for retaining saidvalve member in its said open position once said valve member is movedthereto.
 15. Apparatus adapted to be used in a well bore having at leastone perforated interval traversing earth formations from which connatefluids are to be produced and transported to the surface through astring of production piping supported in the well bore by a wellheadoperatively arranged at the surface for selectively controllingcommunication to the production piping and the well annulus exteriorthereof, said apparatus comprising: an elongated body having alongitudinal bore defining a chamber between the upper and lower ends ofsaid body; first valve means coupled to said upper end of said body andadapted for normally blocking fluid communication between said chamberand a string of production piping coupled thereabove; firstpressure-responsive actuating means operatively associated with saidfirst valve means and adapted for opening said first valve means onlyupon an increase of fluid pressure within a string of production pipingcoupled to said first valve means; second valve means coupled to saidlower end of said body and adapted for normally blocking fluidcommunication between said chamber and a production packer dependentlycoupled therebelow; and second pressure-responsove actuating meansoperatively associated with said second valve means and adapted foropening said second valve means only upon an increase of fluid pressurein the well annulus exterior thereof and above a production packertherebelow.
 16. Apparatus adapted to be used in a well bore having atleast one perforated interval traversing earth formations from whichconnate fluids are to be produced and transported to the surface througha string of production piping supported in the well bore by a wellheadoperatively arranged at the surface for selectively controllingcommunication to the production piping and the well annulus exteriorthereof, said apparatus comprising: first valve means including a firsttubular body adapted to be dependently coupled to the lower end of sucha string of production piping, a fluid barrier sealingly engaged withinsaid first tubular body and adapted for downward movement therefrom toopen communication through said first tubular body, apressure-responsive actuator operatively arranged on said first tubularbody for movement relative thereto between first and second positions,latching means operatively arranged between said actuator and said fluidbarrier for retaining said fluid barrier within said first tubular bodyonly so long as said actuator is in its said first position, and passagemeans on said first tubular body and adapted for communicating pressuretherein above said fluid barrier to said actuator to shift said actuatorto its said second position for releasing said latch means from saidfluid barrier so that said fluid barrier can be moved downwardly fromsaid first tubular body upon an increase of pressure in a productionstring coupled to said first tubular body; a tubular member dependentlycoupled to said first tubular body and having an internal bore adaptedto receive said fluid barrier upon its release from said first tubularbody; and second valve means including a second tubular body dependentlycoupled to said tubular member and adapted for coupling to a productionpacker therebelow for packing-off a perforated interval of a well bore,a transverse barrier arranged within said second tubular body forblocking fluid communication therethrough, upper and lower fluid portsin said second tubular body above and below said transverse barrier, avalve member operatively arranged on said second tubular body andadapted for movement relative thereto between a first position blockingfluid communication between said fluid ports and a second positionestablishing fluid communication therebEtween, and pressure-responsiveactuating means operatively arranged on said second tubular body formoving said valve member to its said second position only upon anincrease of the pressure in the well annulus.
 17. A valve adapted forcoupling to a string of production piping supported in a well boretraversing earth formations and comprising: a tubular body having alongitudinal bore therethrough; a fluid barrier sealingly arranged insaid longitudinal bore and adapted for downward movement therefrom;actuating means slidably mounted on said tubular body and adapted formovement relative thereto between first and second spaced positions;means on said tubular body defining a piston chamber; piston meansoperatively disposed in said piston chamber and adapted for moving saidactuating means from said first position to said second position inresponse to a pressure variation in said piston chamber; latch meansoperatively arranged on said tubular body between said actuating meansand said fluid barrier and adapted for releasably securing said fluidbarrier within said longitudinal bore until said actuating means movefrom said first position to said second position; and passage meansarranged between said piston chamber and said longitudinal bore abovesaid fluid barrier and adapted for communicating pressure variations ina string of production piping coupled to said tubular body to saidpiston means.
 18. The valve of claim 17 further including means operableupon movement of said actuating means to said second position forsecuring said actuating means in said second position.
 19. A valveadapted for coupling to a string of production piping supported in awell bore traversing earth formations and comprising: a tubular bodyhaving a longitudinal bore therethrough; a fluid barrier arranged withinsaid tubular body for blocking fluid communication through saidlongitudinal bore; upper and lower fluid ports in said tubular bodyabove and below said fluid barrier; a tubular valve membertelescopically arranged on said tubular body and adapted for movementrelative thereto between a first position blocking fluid communicationbetween said fluid ports and a second position establishing fluidcommunication therebetween; means on said tubular body defining anannular piston chamber around said lower fluid ports; sealing meansarranged on said valve member and operatively disposed within saidpiston chamber for isolating said lower fluid ports from the exterior ofsaid tubular body so that pressures exterior of said tubular body willbe imposed on said valve member for urging said valve member toward itssaid second position; and means releasably securing said valve memberagainst movement to its said second position until the pressures imposedon said valve member exceed a predetermined value.
 20. The valve ofclaim 19 wherein said fluid barrier is movably disposed in saidlongitudinal bore, and further including means releasably securing saidfluid barrier in said tubular body and adapted to release said fluidbarrier upon application of a predetermined force on said fluid barrier.21. The valve of claim 19 further including means operable upon movementof said valve member to its said second position for securing said valvemember in its said second position.